Friday, May 07, 2010


How IRV screws it up

To answer a question Patrick Ruffini has, here is how ranking a candidate lower in IRV can help them.

Let's say we have three candidates Reagan, Carter, and Anderson, and we have 17 voters.

Let's say, Patrick Ruffini prefers Reagan to Anderson to Carter. 7 other people also have this preference (which we'll call RAC).

Five people prefer Carter to Reagan to Anderson (which we'll call CRA).

Four people prefer Anderson to Carter to Reagan (which we'll call ACR).

To me these seem like possible legitimate breakdowns based on the dynamics of a given race (economic vs. social conservatives, economic vs. social liberals, etc.)

Under IRV, Mr. Anderson is eliminated in the first round because he has the least amount of first place votes. The four voters who ranked him first now transfer their votes to their second choice, Mr. Carter. Mr. Carter now has 9 votes and a majority. He wins 9 to 8 over Mr. Reagan.

But let's say, Mr. Ruffini sees what's going on... See, Ms. Soltis conducted a poll before the election and informed Mr. Ruffini that if they both switched from RAC to ACR (or ARC... doesn't matter), Mr. Anderson would have six first place votes.

Now, Reagan has six first round votes as does Anderson. Mr. Carter is now the candidate eliminated with only five first round votes. With Mr. Carter eliminated, his voters (who ranked CRA) votes are now distributed to their second choice candidate... Mr. Reagan.

Mr. Reagan now has 11 votes and a clear majority. He wins the election thanks to Mr. Ruffini and Ms. Soltis switching their votes.

Note, this happened in the 1990 Ireland election.

I think what IRV ignores is the critical contrasts that develop in a primary or election runoff.

In the first primary or election, name recognition matters more especially in a big field of candidates. Incumbents also run better in the first election.

So IRV actually harms challengers and less known candidates.

If there is a runoff the voters get a second chance to see the differences between two candidates. And usually they vote more against incumbents and front runners when this happens.

IRV prevents this from happening.
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